The purposes of this research are to determine if there are long-term consequences of increased lead absorption in children and to evaluate the current criteria for treatment of lead overexposed children. Existing studies of neuropsychologic sequelae to low-level lead overexposures have yielded inconsistent results. The present research will utilize a twin methodology to control for exposures to environmental risk factors other than lead and to control for genetic and cultural factors which might otherwise lead to confounding in outcome measures such as intelligence quotients. Members of twin pairs with a history of increased lead absorption will be compared with less-exposed twin siblings on a number of neuropsychological measures and school performance. The population of twins will be obtained from the records of the New York City Bureau of Lead Poisoning control. Premorbid conditions will be determined from birth records, hospital/doctors records, and from parental interviews.